A 17-year-old girl died days after Christmas, an inquest heard.
Medical experts are at a loss to explain the death of Kasia Margaret Ber, of Horden, near Peterlee, east Durham, after she was taken to hospital.
An inquest in Durham City heard that the teenager was found at home by her family at 7.10am on Wednesday. She appeared to be having problems breathing.
An ambulance was called, but she died in hospital later that morning.
The inquest was told that the student, who had a part-time job as a sales assistant, had been to see her GP on December 9 complaining of heart palpitations.
She was put on a heart monitor, but the tests came back normal. She was awaiting the results of blood tests
Her father, John Joseph Ber, told the inquest she began feeling poorly two weeks ago.
The inquest was adjourned.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article